With the development of communication technology, the demand for data services continues to increase. This stimulates the communications industry to increase the research for wireless systems, so the wireless system operators proceed to do further researches for bandwidth enhancement and higher carrier frequency. For example, the fifth generation of mobile communication system (5G) will have its wireless access utilizing frequencies including millimeter-waves (abbreviated as mm-waves) so as to provide multi-gigabit-per-second data rates in the deployment of microcells, femtocells, or macrocells. Although free space propagation or path loss increases as frequencies become higher, the path loss can be compensated by using antenna directivity. The path loss compensation can be implemented by using a solution of high-gain adaptive beamforming. An adaptive beam steering can be implemented by using analog phase shifters, or combination of digital and analog solutions such as making fully-digital transmission/receiving paths, each of which is provided for an antenna, being connected to a set of antennas. The base station antenna array can include 8, 16, 32, 64, or more antenna elements (e.g., micro horn antennas).
The millimeter-waves having frequencies, for example, 11 to 300 GHz, which are higher than the frequencies used by conventional wireless systems are utilized. The so-called millimeter-waves are electromagnetic waves having frequencies lying among those of the microwaves and the light waves, usually in the millimeter-wave band from 30 to 300 GHz, corresponding to wavelengths between 1 to 10 mm. The millimeter waves can provide a wider frequency band. With the rapid growth of data transfer rates, it is expected that data transfer rates will increase 1000 times by 2020, and 10,000 times by 2025, after the beyond 4G era (Beyond 4G or B4G). Among others, the transmission technology based on millimeter wave (mm-wave) spectrum has been regarded as one of the key communication technologies capable of providing high data transfer rates, and will be playing a pivotal role in the beyond 4G era and even the fifth generation (5G) communication technology development.
A U.S. patent application publication, US2004/0214606 A1, relates to a method and a communication system wherein stations communicate on a wireless interface. The method includes the steps of including beam identity information into signals transmitted on multiple beams provided by a first station; receiving at a second station signals transmitted from the first station; and identifying beams via which the second station received signals from the first station based on the identity information. At least one beam for transmission on the wireless interface between the stations is then selected. A station configured for the communication comprises antenna means for receiving signals transmitted from the other station on multiple beams and a controller for identifying beams based on beam identity information associated with signals received from the other station.